In the field of gas distribution, there has always been a request from customers for position signalling devices to check, from a remote station, the open or closed status of apparatuses, such as the means for controlling the flow, which are located, for example, inside a gas regulating station.
In this description, the expression control elements is used to mean both devices for regulating the flow of gas and devices for safely blocking the flow of gas.
In other words, the expression flow control means is used to mean pressure regulating devices and also safety devices of both the analogue and on-off type.
The above-mentioned regulating stations are in fact spread throughout the territory and cannot be physically manned by an operator who continuously checks the correct operation.
Currently, this signalling is performed by switches which are directly connected to the mechanical detection of the position of the shutter of the control element.
A type of switch (proximity switch) detects when a metal mass approaches.
In other words, by directly associating the movement of a mechanical stroke indicator of the shutter of the element for controlling the flow to a metal plate which positions itself close to this switch, the latter emits a signal signifying the position of the stroke indicator and, therefore, the closed/open state of the control element.
To all intents and purposes, it is a proximity sensor.
Another type of switch (microswitch) comprises the physical activation of a pushbutton which, also activated by the above-mentioned plate integral with the above-mentioned stroke indicator, signals one situation or the other.
In other words, in both these prior art solutions a mechanical connection is currently made between the element for controlling the flow and the switch.
Thus, in both these solutions, a rod or similar metal part protrudes from the body of the control element, connected directly and mechanically to the body of the control element (pressure regulating valve or block valve) for detecting a posteriori the state of the shutter.
The creation of this mechanical connection allows a detection a posteriori of the effect requested by the variation or fault of the parameter controlled (pressure downstream of the station) and only in the case of correct operation of the shutter of the control element.
Moreover, in practical cases, the creation of this mechanical connection implies the drawback of having to make a series of variants as a function of both the shape and size of the control element and the space available in the surrounding environment.
In short, it is necessary to customise the connection between the switch and the control element for each specific situation, using suitable and special mechanical solutions, such as brackets plates, rods etc.
Moreover, since the prior art systems are positioned outside the control element, even if they are not necessarily exposed to the adverse weather conditions of the outside environment, they are nevertheless exposed to environmental conditions which are not always necessarily favourable (for example, formation of condensate which facilitates rusting).
Moreover, the fact that the above-mentioned switch is any case powered electrically, and rigidly connected to the body of the control element, implies the further drawback that the control element complete with integral switch is classified as an assembly and must therefore be internationally compliant with legally binding and without doubt stricter safety regulations.
Further, the normal signalling systems are based on the stroke of the shutter element of the control element to indicate whether the element is operating or not. Sometimes, however, the stroke of the shutter (to enter regulating mode) is so small, even in the range of a few tenths of a millimeter, that its measurement by a mechanical detector may be completely imprecise or even not detected, if the above-mentioned movement is less than the sensitivity of the detector.